Aedes aegypti mosquitoes from several locations in Asia, Africa, southern USA, and Caribbean will be tested for vector competence with yellow fever virus. The rate of yellow fever transovarial transmission after the first ovarian cycle will be determined. An attempt will be made to develop the RIA detection technique for yellow fever antigens in mosquito expectorate. The pathogenesis of Mokola virus in Aedes mosquitoes will be studied using virus titration and FA methods. Emphasis will be on establishing a passage line in reproductive tissues. The development of antibody for Congo-Crimean hemorrhagic virus in laboratory animals will be followed by FA, AGDP, CF, and HI tests. The plaque reduction neutralization test and in vitro immunologic methods in CER cells, will be used to compare virus strains from different geographic areas. Comparison of strains will also be attempted using glycoproteins and biochemical techniques.